1. Field of the Invention
The present invention relates to a display device comprising an element (hereinafter referred to as a light-emitting element) in which a light-emitting material is interposed between a pair of electrode, and to a method of manufacturing thereof. More particularly, the present invention relates to a sealing structure of a display device using a light-emitting material that generates electroluminescence (EL) and a method of manufacturing the same.
2. Description of the Related Art
In recent years, development of a display device (EL display device) using a light-emitting element (hereinafter referred to as an EL element) which utilizes electroluminescent phenomenon of a light-emitting material has been advanced. Since the light-emitting element of the EL display device is a self-luminous type, a backlight, which is used for a conventional liquid crystal display device, is unnecessary. In addition, the EL display device has merits of the wide viewing angle, the excellent visibility and the like.
It has been said that the EL element emits photons as follows. By applying a voltage to an organic compound layer interposed between a pair of electrodes, electrons injected from a cathode and positive holes injected from an anode recombine together at a center of luminescence in the organic compound layer to form excited molecules, and hence, energy is released to emit photons when the excited molecules return to the base state. There are known two different excited states: a singlet excited state and a triplet excited state. Luminescence can be generated through either of the states.
Although there are inorganic light-emitting materials and organic light-emitting materials as the material used for the EL element, the organic light-emitting materials so which can be driven at lower voltage than the inorganic light-emitting materials has been attracting much attention.
However, when the EL element comprising an organic material is driven for a certain period, luminance and light emitting properties such as nonuniformity of light emission are drastically deteriorated as compared with those in the initial state, which results in a problem of low reliability. The low reliability of the EL element is a limiting factor in practical application of the EL material.
Further, moisture and oxygen which penetrate from outside into the EL element are another factor of deteriorating the reliability of the EL element.
In an EL display device (panel) using an EL element, moisture penetrating into the interior of the device causes a serious degraded reliability, which further reads to a dark spot, shrinkage, and deterioration in luminance from a periphery of The EL display device. The dark spot is a phenomenon in which luminance is partly degraded (which includes nonluminous portion), and is generated when a hole is formed in an upper electrode. Meanwhile, the shrinkage is a phenomenon in which luminance is deteriorated from edges of a pixel.
Accordingly, a display device comprising a structure for preventing the above-mentioned deteriorations of the EL element has been researched and developed. In order to prevent the foregoing problems, there is a method in which the EL element is accommodated in an airtight container and a desiccant is provided in an airtight space (for ample, see patent document 1).